Male Reproduction Flashcards
present at birth (internal and external genitalia)
primary sex characteristics
emerge during puberty
secondary sex characteristics
gene on the Y
chromosome directs
male development
SRY gene
Two principal functions of the testes
sperm production
testosterone synthesis
Testes are primarily
regulated by the
Hypothalamic-Pituitary-
Gonadal (HPG) axis
secreted in a pulsatile
manner and causes the release of both LH and FSH
GnRH
favored with fast pulses of GnRH
LH
favored with slow pulses of GnRH
FSH
GnRH output altered by environmental and social factors
day length, stress, negative feedback from steroids, nutrition, ambient temperature, and the presence of a reproductive partner
a major regulator of GnRH neurons
KISS neuron
relay signals from
the periphery to GnRH neurons to regulate
KISS neurons and GnIH
receive signals about energy balance and convey this to GnRH neurons to regulate HPG axis activity
KISS neurons in the arcuate nucleus
KISS neurons have receptors for:
Leptin - high leptin/energy = positive signal from KISS neurons
ghrelin- low energy/low ghrelin = no signal from KISS neurons
Sex steroids regulate
GnRH indirectly through
KISS neurons
Puberty begins when
GnRH secretion is triggered by KISS
Maturation of Sertoli and Leydig Cells
puberty
stimulates spermatogenesis
(sperm production) in
Sertoli cells
FSH
stimulates
steroidogenesis in
Leydig cells
LH
Testosterone is produced by the interstitial blank cells, which lie in clusters between the seminiferous tubules
leydig cells
the principal role is the synthesis and secretion of testosterone
leydig cells
Comprised of supporting cells (Sertoli cells) and developing sperm cells
Seminiferous Tubules
Sperm are formed and develop within
Seminiferous Tubules
are needed for maximal sperm production
testosterone from Leydig cells
FSH
sperm cell development through mitotic and meiotic divisions and finally a metamorphic change to produce spermatozoa
Spermatogenesis
takes ~72 days but sperm
are produced
continuously (>200
million/day)
Spermatogenesis
support and nourish the immature sperm cell in Seminiferous Tubules by giving them nutrients and blood products
sertoli cells
seminiferous tubule cell developing into sperm
Spermatocytes
seminiferous tubule cells that are stem cells
Spermatogonium
stimulates Sertoli cell functions
are the only cells with FSH receptors in human males
FSH
Secretes androgen-binding protein (ABP) = carrier protein that concentrates
testosterone in testes
sertoli cells
Produce nutrients for sperm
sertoli cells
Forms the blood-testis barrier
sertoli cells
Secretes inhibin
sertoli cells
physical barrier between seminiferous tubules and
blood vessels; formed by tight junctions between Sertoli cells
Blood-testis barrier
isolate differentiating sperm cells from the bloodstream
Blood-testis barrier
Protein hormone secreted from Sertoli cells in response to FSH
inhibin
Concentration in blood is reflective of the number of functioning
Sertoli cells and spermatogenesis
inhibin
the primary testicular factor regulating FSH
Inhibits transcription of the gene encoding the β-subunit of FSH
Inhibin B
The principal steroid hormone (aka androgen) produced from testes
testosterone
Transported via carrier proteins:
-SHBG (sex-hormone binding globulin)
-Albumin
Binds to intracellular androgen receptor
testosterone
Maturation of Reproductive Organs and
Secondary Sex Characteristics
puberty
Effects of puberty
- Pubic/facial hair & oil glands emerge
- Reproductive tissues enlarge
- Increased muscle mass (upper torso)
- Larynx enlarges & vocal cords thicken
- Increased sexual behavior (libido)
Absence of testicular enlargement by age 14
-Causes: genetic delay in HPG axis development,
undernutrition, or illness
Development can be delayed for several years and eventually
occur normally (“constitutional delay”)
Delayed/Deficient Puberty
Functional or persistent hypogonadism (low testosterone)
requires hormone replacement therapy due to
Delayed/Deficient Puberty
Early puberty (< age 9 in males)
Causes: premature activation of HPG axis,
increased sensitivity to LH/FSH, or a tumor
disrupting negative feedback
Premature/rapid early growth leads to shorter stature as adults
Treatment – puberty blockers (suppress LH and FSH)
Precocious Puberty
Functions of Testosterone & its Metabolites in Adults
- Maintains secondary sex traits
- Sperm production
- Stimulate and maintain bones
- Stimulate sexual behaviors
- Negative feedback (primarily
estrogen)
ow testosterone that can cause infertility
hypogonadism
decreases secretion of GnRH
obesity
Progressive decline in testosterone
starting ~40 yrs. and sperm production
drops ~30%
old age
decline in testosterone
production with age
Andropause
Anabolic androgenic steroids (AAS) are a
synthetic version of testosterone that
enhance androgenic effects, like larger
muscle mass, but you also get…
* Breast enlargement
* Reduced testicular size
* Low sperm count (infertility)
sex steroids to increase testosterone
Effects of anabolic androgenic steroids on fertility
most likely will make you infertile
